This invention relates to a composite material, a method of making the composite material and a method of making a tool component.
Polycrystalline diamond (herein referred to as PCD) and polycrystalline cubic boron nitride (herein referred to as PcBN) are well known materials used in cutting and abrasive applications. PCD cutters are well-known and widely used in drill bit technology as the cutting element in drill bits used in core drilling, oil and gas drilling, and other similar applications. Such cutters generally comprise a PCD table formed on a hard metal substrate by a high temperature—high pressure sintering process. The substrate is then either brazed on an elongated support, or is directly brazed in a pocket of the drill bit, in a manner that exposes the PCD table to the surface for rock cutting.
It is known that PCD cutters with a thick PCD table can enjoy a prolonged useful life during the drilling operation. This is simply due to the fact that there is more of the ultrahard phase available for performing the rock cutting and shearing operation. However, a cutter with a thick PCD table layer, once a wear scar is formed, attacks the rock by applying the cutting loads on the rock through the part of the PCD table that is in contact with it. If the PCD layer is much thicker than those found in conventional cutters, then the cutting loads are distributed over a large area on the face of the rock being engaged. Therefore the cutting stresses are low, and the cutting efficiency is reduced. An engineering solution to maintaining a sharp edge is proposed by U.S. Pat. No. 5,301,762 to Besson, in which propositioned grooves are placed in the structure, in order to generate a chipping effect that will generate a sharp fresh cutting edge. Such a technique uses up a significant proportion of the cutter's useful PCD material by fracturing it away, and cannot be cost effective.
In EP 0 196 777 to Wardley a way of maintaining sharpness of the PCD table by grading the wear resistance of said table is proposed. Specifically, the top layer is made of more wear resistant material than the layer adjacent to the substrate of the drilling cutter. The result is that the PCD layer below the top surface wears faster than the top layer, thus giving rise to a lip. This development generates a self-sharpening effect. The improved wear resistance is typically achieved by making the top PCD layer out of a fine grained PCD, and/or by reducing the amount of binder material used in comparison to the amount used to make less wear resistant layers. However, such thick PCD layers, when they contain fine grain diamond, are difficult to infiltrate with the necessary binder material. Therefore such cutters are difficult to sinter.
It is claimed in U.S. Pat. No. 4,311,490 that such problems can be overcome by using coarse diamond particles as the starting material for the PCD layers adjacent to the substrate. Although such an approach helps, it does not eliminate the problem of infiltrating the top fine-grained layers, which in modern cutters can have substantial thickness. As such PCD tables become thicker, toughness of the PCD table becomes increasingly important, due to the volume effect associated with the fracture probability of brittle materials. A number of disclosures deal with this problem.
In U.S. Pat. No. 6,361,873 to Siracki et al an ordered structure of two phases that enhances the material's chipping resistance is disclosed. This is a very general patent, and does not address any other aspect than toughness of a structure. In U.S. Pat. No. 4,604,106 it is suggested that the admixing of two phases in a random, but graded manner can be used to address stress management, as well as toughening of the structure. U.S. Pat. No. 6,06,352 to Rai and U.S. 2002/194955 disclose coated fibre and granule structures, respectively, in order to generate tough structures. In both the fibres and the granules, the core is made from ultrahard polycrystalline based materials, while the rim is made from. Hard metals or cermets. In all these cases, these advantages are attained at the sacrifice of wear resistance, as a result of the introduction of the less wear resistant cermets.